1. Field of the Invention
The present invention relates to a liquid crystal display device that has reflective and transparent electrodes and that is illuminated with transmitted and reflected light, and to a method for fabricating such a liquid crystal display device.
2. Description of Related Art
Thin and power-saving, liquid crystal display devices find wide application in office automation equipment such as personal computers, in personal digital assistant equipment such as electronic personal organizers and cellular phones, and in other equipment such as VCRs incorporating a camera. Liquid crystal display devices are classified into a transmissive type, which uses as pixel electrodes a transparent conductive film such as one formed of ITO, and a reflective type, which uses as pixel electrodes reflective electrodes such as those formed of a metal.
Transmissive liquid crystal display devices provide display while being illuminated with a backlight. This advantageously permits bright, high-contrast display, but disadvantageously results in high electric power consumption. By contrast, reflective liquid crystal display devices are illuminated with ambient light, and thus do not require a backlight. This advantageously contributes to low electric power consumption, but disadvantageously leads to low contrast depending on ambient brightness. For these reasons, semi-transmissive liquid crystal display devices have come into practical use that can be illuminated both with reflected ambient light and with the light from a backlight.
Japanese Patent Application Laid-open No. 2000-111902 discloses a semi-transmissive liquid crystal display device. FIG. 21 is a sectional view of this liquid crystal display device. The liquid crystal display device 1 has a backlight 3 provided on the back side of a display panel 2. The display panel 2 has liquid crystal 6 sealed between a pixel substrate 4 and a opposed substrate 5. The pixel substrate 4 has a base coat film 32 formed on a glass substrate 31.
On the base coat film 32 is formed a semiconductor layer 33, which functions as a TFT element having a gate G, a source S, and a drain D. On top of the semiconductor layer 33 is formed a gate insulation film 35, and further on the gate insulation film 35 is formed a gate electrode 36. On the gate electrode 36 is formed an interlayer insulation film 37. A source electrode 38 and a drain electrode 39 are formed so as to conduct to the source S and the drain D, respectively, through contact holes 37a formed in the interlayer insulation film 37.
On the interlayer insulation film 37 is formed a transparent resin layer 40, and further on the transparent resin layer 40 is formed a transparent electrode 41. The transparent electrode 41 is formed of, for example, ITO, and conducts to the drain electrode 39 through a contact hole 40a formed in the transparent resin layer 40. In a predetermined place on the transparent electrode 41, a reflective electrode 42 is formed that is formed of, for example, aluminum. The transparent electrode 41 and the reflective electrode 42 together form a pixel electrode 10. In the entire liquid crystal display device 1, a large number of pixel electrodes 10 are arrayed in a matrix. The pixel electrode 10 thus has a reflective portion 10a, which is formed by the reflective electrode 42, and a transmissive portion 10b, which is formed by the portion of the transparent electrode 41 lying elsewhere than in the reflective portion 10a. 
The opposed substrate 5 has a coloring layer 22 formed on a glass substrate 21. The coloring layer 22 functions as a color filter for adding a color to light. On top of the coloring layer 22 is formed a opposed electrode 23 formed of, for example, ITO. On the transparent electrode 41 and the opposed electrode 23 are formed alignment films (not illustrated) for aligning the liquid crystal 6.
In the liquid crystal display device 1 structured as described above, when the backlight 3 is lit, the light emitted from the backlight 3 travels through the transmissive portion 10b and illuminates the display panel 2. When the backlight 3 is off, ambient light enters the display panel 2, and is then reflected on the reflective portion 10a to illuminate the display panel 2. In this way, the displayed image is made comfortably visible. The coloring layer 22 has, in the part thereof opposite the reflective portion 10a, an opening 22a. The opening 22a helps obtain sufficient brightness when illumination is achieved by reflection.
The conventional liquid crystal display device 1 described above, however, has the following disadvantages. As increasingly high-resolution display panels 2 are used, when the glass substrates 21 and 31 contract under the influence of the heat and membrane stress to which they are exposed during the fabrication process, it has been becoming increasingly difficult to accurately position the pixel electrode 10 formed on the pixel substrate 4 relative to the coloring layer 22 formed on the opposed substrate 5. This lowers the aperture ratio and the yield of the liquid crystal display device 1.